I've been working with Telerik AppBuilder for the past few weeks, and so far I've found it quite user friendly and powerful.
PROS: There are a lot of sample apps in the Telerik site to check for examples and source code, so you'll surely find something that can help you build prototype applications fast. If you're a Visual Studio user, you can greatly benefit from the VS Extension that lets you build apps using the VS IDE.
CONS: AppBuilder uses some native styles for different devices, so if you want to have a consistent design throughout many platforms you'll have to mess with some CSS to override the default styles. The greatest caveat is that if your app needs to show a lot of information in one view (like an endless scrolling view) the app may crash for lack of system memory, although there are workarounds to this. Also, if you need the Visual Studio Extension the monthly cost goes up considerably.
Since it has a 30-day free trial (which is also good for the VS Extension), I think you have nothing to lose by downloading it and see if it suits your needs.